The present invention is related to the field of network communications devices such as switches and routers, and more particularly to techniques by which network communications devices receive operating power.
Network communications devices such as switches and routers conventionally include a power supply which provides operating power at a specified DC voltage from an external source of AC (or in some cases DC) power, such as so-called “mains power” provided from a building power distribution system. A power supply for a device may be designed and sized to meet particular goals, for example to provide a desired degree of availability (reliable operation over time) and to accommodate a reasonably foreseeable highest load that might occur, for example due to incrementally adding circuit boards or other loads to the device as system needs change with time. Availability is sometimes provided in the form of redundancy, where a failed power supply can be replaced with another “standby” or “backup” power supply included either within or external to the network communications device for just that purpose.
There is widespread use of so-called power-over-Ethernet (POE) technology, in which terminal devices such as IP telephones receive operating power from power-sourcing equipment (PSE) device such as a switch over the same Ethernet cables used for communications. A switch functioning as a PSE device includes one or more power supplies that provide both operating power for the switch as well as power to powered POE ports connected to powered devices by Ethernet cable. Thus, the sizing and other design/configuration criteria for power supplies in PSE devices generally must take into consideration the potential for growth and other changes in an overall system including all POE powered devices. One general approach has been to include relatively large-capacity power supplies in PSE devices to provide sufficient capacity for current and expected future POE loads. Another approach has been to dedicate space within PSE devices for accepting an additional power supply at a later time as needs grow. Additionally, in the case of systems requiring high availability, redundancy is typically provided in the form of one or more “backup” power supplies, located either within or external to POE switches.